-软件工程实践者的研究方法课件.ppt

1、1Chapter 8nDesign ConceptsSoftware Engineering:A Practitioners Approach,7/e by Roger S.Pressman2DesignnGood software design should exhibit:nFirmness(稳定性):A program should not have any bugs that inhibit its function.nCommodity(适用性):A program should be suitable for the purposes for which it was intend

2、ed.nDelight(令人愉快):The experience of using the program should be pleasurable one.3Analysis Model=Design ModelAnal ysi s M odeluse-cases-t ext use-case di agr am s act i vi t y di agr am s swi m l ane di agr am sdat a f l ow di agr am s cont r ol-f l ow di agr am s pr ocessi ng nar r at i vesf fl lo o

3、w w-o or ri ie en nt te ed d e el le em m e en nt ts sb be eh ha av vi io or ra al le el le em m e en nt ts sc cl la as ss s-b ba as se ed de el le em m e en nt ts ss sc ce en na ar ri io o-b ba as se ed de el le em m e en nt ts scl ass di agr am s anal ysi s packages CRC m odel s col l abor at i on

4、 di agr am s st at e di agr am s sequence di agr am sD D a at ta a/C Cl la as ss s D D e es si ig gn nA A r rc ch hi it te ec ct tu ur ra al l D D e es si ig gn nI In nt te er rf fa ac ce e D D e es si ig gn nC Co om m p po on ne en nt t-L Le ev ve el l D D e es si ig gn nDesi gn Model43 Characters

5、of Design Qualitythe design must implement all of the explicit(明确的)requirements contained in the analysis model,and it must accommodate all of the implicit(隐含的)requirements desired by the customer.the design must be a readable,understandable guide for those who generate code and for those who test a

6、nd subsequently support the software.the design should provide a complete picture(全貌)of the software,addressing the data,functional,and behavioral domains from an implementation perspective.5Quality GuidelinesA design should exhibit an architecture that(1)has been created using recognizable architec

7、tural styles or patterns,(2)is composed of components that exhibit good design characteristics and(3)can be implemented in an evolutionary fashionA design should be modular;that is,the software should be logically partitioned into elements or subsystemsA design should contain representations of data

8、,architecture,interfaces,and components.A design should lead to data structures that are appropriate for the classes to be implemented.A design should lead to components that exhibit independent functional characteristics.A design should lead to interfaces that reduce the complexity of connections b

9、etween components and with the external environment.A design should be derived using a repeatable method that is driven by information obtained during software requirements analysis.A design should be represented using a notation that effectively communicates its meaning.6Design PrinciplesThe design

10、 should be traceable to the analysis model.The design should not reinvent(彻底改造)the wheel.The design should“minimize the distance”between the software and the problem as it exists in the real world.The design should exhibit uniformity and integration.The design should be structured to accommodate cha

11、nge.The design should be assessed for quality as it is being created,not after the fact.The design should be reviewed to minimize conceptual(semantic)errors.Design is not coding,coding is not design.From Davis DAV957Fundamental ConceptsnAbstractiondata,procedurenArchitecture(架构)the overall structure

12、 of the softwarenPatternsconveys(承载)the essence(精髓)of a proven design solutionnModularitycompartmentalization(划分)of data and functionnInformation hidingcontrolled interfacesnFunctional independencesingle-minded function and low couplingnAspectsa mechanism for understanding how global requirements af

13、fect designnRefactoring(重构)a reorganization technique that simplifies the designnDesign Classesprovide design detail that will enable analysis classes to be implemented8Data Abstractionimplemented as a data structure9Procedural Abstractionimplemented with a knowledge of the object that is associated

14、 with enter10ArchitectureStructural properties.Extra-functional properties.Families(族族)of related systems.11ArchitecturenIn the simplest form,architecture is the structure or organization of program components(modules),the manner in which these components interact,and the structure of data that are

15、used by the components.nIn a broader sense,components can be generalized to represent major system elements and their interactions.12Modularitynmodularity is the single attribute of software that allows a program to be intellectually manageable.nMonolithic(整块庞大的)software(i.e.,a large program compose

16、d of a single module)cannot be easily grasped()by a software engineer.nThe number of control paths,span of reference(引用跨度),number of variables,and overall complexity would make understanding close to impossible.nIn almost all instances,you should break the design into many modules,hoping to make und

17、erstanding easier and as a consequence,reduce the cost required to build the software.13Modularity:number of modules 14Why Information Hiding?nreduces the likelihood of“side effects”nlimits the global impact of local design decisionsnemphasizes communication through interfacesndiscourages the use of

18、 global datanleads to encapsulationan attribute of high quality designnresults in higher quality software15Information Hiding16Sizing Modules:Two ViewsMODULEWhats inside?How big is it?17Functional IndependencenFunctional independence is achieved by developing modules with single-minded function and

19、an aversion to excessive interaction with other modules.nCohesion(内聚性)is an indication of the relative functional strength of a module.nA cohesive module performs a single task,requiring little interaction with other components in other parts of a program.Stated simply,a cohesive module should(ideal

20、ly)do just one thing.nCoupling(耦合性)is an indication of the relative interdependence among modules.nCoupling depends on the interface complexity between modules,the point at which entry or reference is made to a module,and what data pass across the interface.18AspectnAn aspect is a representation of

21、a cross-cutting concern.(横切关注点:利用“横切”技术，剖开封装的对象内部，将那些影响多个类的公共行为封装成一个可重用对象，称为Aspect)。nConsider two requirements A and B.B crosscuts A if a software decomposition has been chosen in which A cannot be satisfied without taking B.nAOP(Aspect Oriented Programming)是OOP的补充和完善。n如：业务处理的主要流程是核心关注点，与之关系不大的部分是横切

22、关注点,如权限认证、日志、事务处理等，可以将核心关注点和横切关注点分离开来。19显示更新的需求：显示更新的需求：无论图元何时移动、无论图元何时移动、移动到哪里，都要移动到哪里，都要通知屏幕管理器通知屏幕管理器（Display）其位）其位置发生了改变。置发生了改变。Aspect-Example20 采用采用OOPOOP，典型做法是在每个移动图元的操作代码中，插入一段通知，典型做法是在每个移动图元的操作代码中，插入一段通知Display其位置发生改变的代码，即：调用其位置发生改变的代码，即：调用Display.update()。Class Line private Point _p1,_p2;Po

23、int getP1()return _p1;Point getP2()return _p2;void setP1(Point p1)this._p1=p1;Display.update();void setP2(Point p2)this._p2=p2;Display.update();Class Point private int _x1,_x2;int getX()return _x1;int getY()return _x2;void setX(int x1)this._x1=x1;Display.update();void setY(int x2)this._x2=x2;Display

24、.update();Aspect-Example21Aspect DisplayUpdatingPointcut move():call(void Line.setP1(Point)|call(void Line.setP2(Point)|call(void Point.setX(int)|call(void Point.setY(int);after()returning:move()Display.update();Class Line private Point _p1,_p2;Point getP1()return _p1;Point getP2()return _p2;void se

25、tP1(Point p1)this._p1=p1;void setP2(Point p2)this._p2=p2;Class Point private int _x1,_x2;int getX()return _x1;int getY()return _x2;void setX(int x1)this._x1=x1;void setY(int x2)this._x2=x2;采用采用AOPAOP，典型做法是在将所有移动图，典型做法是在将所有移动图元的代码封装成一个元的代码封装成一个Aspect:Aspect:DisplayUpdating。Aspect-Example22AspectAn Ex

26、amplenConsider two requirements for the SafeHomeAssured WebApp.Requirement A is described via the use-case Access camera surveillance via the Internet.A design refinement would focus on those modules that would enable a registered user to access video from cameras placed throughout a space.Requireme

27、nt B is a generic security requirement that states that a registered user must be validated prior to using SafeHomeAssured.This requirement is applicable for all functions that are available to registered SafeHome users.As design refinement occurs,A*is a design representation for requirement A and B

28、*is a design representation for requirement B.Therefore,A*and B*are representations of concerns,and B*cross-cuts A*.nAn aspect is a representation of a cross-cutting concern.Therefore,the design representation,B*,of the requirement,a registered user must be validated prior to using SafeHomeAssured,i

29、s an aspect of the SafeHome WebApp.23RefactoringnRefactoring is the process of changing a software system in such a way that it does not alter the external behavior of the code design yet improves its internal structure.nWhen software is refactored,the existing design is examined for nredundancynunu

30、sed design elementsninefficient or unnecessary algorithmsnpoorly constructed or inappropriate data structuresnany other design failure that can be corrected to yield a better design.24The Design Modelp p r ro o c ce es ss s d d i im m e en ns si io o n narchi tecture el em entsi nterface el em entsc

31、om ponent-l evel el em entsdepl oym ent-l evel el em entsl owhi ghcl ass di agram s anal ysi s packages C RC m odel s col l aborati on di agram s use-cases-text use-case di agram s acti vi ty di agram s sw i m l ane di agram s col l aborati on di agram sdata fl ow di agram s control-fl ow di agram s

32、 processi ng narrati vesdata fl ow di agram s control-fl ow di agram s processi ng narrati vesstate di agram s sequence di agram sstate di agram s sequence di agram sdesi gn cl ass real i zati ons subsystem s col l aborati on di agram s desi gn cl ass real i zati ons subsystem s col l aborati on di

33、agram s refi nem ents to:depl oym ent di agram scl ass di agram s anal ysi s packages C RC m odel s col l aborati on di agram s com ponent di agram s desi gn cl asses acti vi ty di agram s sequence di agram srefi nem ents to:com ponent di agram s desi gn cl asses acti vi ty di agram s sequence di ag

34、ram sdesi gn cl ass real i zati ons subsystem s col l aborati on di agram s com ponent di agram s desi gn cl asses acti vi ty di agram s sequence di agram sa a n n a a l ly y s si is s m m o o d d e e l ld d e e s si ig g n n m m o o d d e e l lRequi rem ents:constrai nts i nteroperabi l i ty target

35、s and confi gurati ontechni cal i nterface desi gn N avi gati on desi gn G U I desi gn 25Design Model ElementsnData elementsnData model-data structuresnData model-database architecturenArchitectural elementsnApplication domainnAnalysis classes,their relationships,collaborations and behaviors are tra

36、nsformed into design realizationsnInterface elementsnComponent elementsnDeployment elements26Architectural ElementsnThe architectural model is derived from three sources:ninformation about the application domain for the software to be built;nspecific requirements model elements such as data flow dia

37、grams or analysis classes,their relationships and collaborations.nthe availability of architectural patterns.27Interface ElementsControl PanelLCDdi spl ay LEDi ndi cators keyPadCharacteri sti cs speaker wi rel essI nterface readKeyStroke()decodeKey()di spl ayStatus()l i ghtLEDs()sendControl M sg()Fi

38、 gure 9.6 UM L i nterface representati on for C Co on nt tr ro ol lP Pa an ne el lKeyPadreadKeystroke()decodeKey()W i rel essPDAKeyPadM obi l ePhoneuser interface external interfaces to other systems,devices.-include checking and definitive information about the information is sent or received(3)int

39、ernal interfaces between various design components.-an interface is a set of operations that describes some part of the behavior of a class and provides access to these operations.28Interface Elements29Component ElementsSensorManagementSensorn component-level design defines data structures for all l

40、ocal data objects and algorithmic detail for all processing that occurs within a component and an interface that allows access to all component operations.30Deployment ElementsF i g u re 9.8 U M L d e p l o y m e n t d i a g ra m fo r S a fe H o m ePersonal com puterSecuri tyhom eM anagem entSurvei l l ancecom m uni cati onC o n tro l P a n e lC P I se rv e rSecuri tyhom eow nerA ccessexternal A ccessn Indicate how software functionality and subsystems will be allocated within the physical computing environment